The present invention relates to a hydraulic gear pump of the type which includes a toothed internal gear and a mating toothed external or pinion gear, and wherein the teeth define fluid cells which are alternately expanded and compressed upon rotation of the gears. Such gear pumps are commonly used as the lubricating oil pump for the internal combustion engine of an automobile.
The internal combustion engine of an automobile operates under unique conditions, in that it is operated at very different and constantly changing operating speeds and loads, starting with the idling speed and ending with the maximum operating speed under heavy load. The lubricating oil system must therefore satisfy the maximum load conditions, but at the same time it should not unnecessarily consume energy at the lower speed and load ranges.
The internal combustion engine of an automobile should also meet the further requirement of long service life, without requiring extensive maintenance. This is rendered difficult by the face that the engine is subject to wear, which leads to an increased consumption of the lubricating oil, and to a pressure drop in the lubricating oil system. The oil pump must therefore be adapted to this increasing need during the service life of the engine, and this increased capacity results in a corresponding energy loss during times when the increased capacity is not required.
The above cited copending applications describe a lubricating oil system which delivers an adequate quantity of the lubricating oil under all operating conditions, and yet avoids losses from excessive capacity. More particularly, the copending applications describe an internal gear pump wherein the teeth interengage so as to define fluid cells which are alternately expanded and compressed upon rotation of the gears. Preferably at least three cells of decreasing volume define the outlet zone, and a number of ports extend through the wall of the housing and which correspond in number to the number of decreasing cells. Some or all of these outlet ports terminate in the lubricating oil outlet passage, and those ports which are associated with the cell having the greatest volume include a non-return valve. Thus only the ports associated with the smallest fluid cells may directly communicate with the outlet passage and without a non-return valve. An internal gear pump of the described type is also illustrated in DE-OS Nos. 34 44 859 and 35 06 629.
In the above cited copending applications, a throttling means is positioned in the fluid inlet line. More particularly, a fixed throttle is positioned in a first fluid line leading to the inlet port from an oil tank, and there is further provided a by-pass line which is parallel to the first line. A pressure controlled throttle valve is positioned in the by-pass line, which is controlled by the outlet pressure of the lubricating oil pump, and which in turn controls flow through the by-pass so that the by-pass closes when the pressure in the fluid outlet of the pump reaches a predetermined valve. In this arrangement, the throttle in the first fluid line is designed so that the quantity of the lubricating oil which is delivered by the pump is dependent on the speed only up to a predetermined speed. This takes into account the fact that the lubricating oil consumption of the engine is dependent on the speed in the lower speed ranges. However, it is believed that the dependency of the lubricating oil consumption on speed exists only up to a certain threshold speed, and the throttle is dimensioned in accordance with this speed. Further, the lubricating oil system may be adapted to any increased additional requirement which may, for example, be required by wear, in that the resulting pressure drop may be used for opening the by-pass line. The opening of the by-pass line permits the entire delivery capacity, or an additional portion of the delivery capacity, of the lubricating oil pump to be made available.
It is an object of the present invention to provide a lubricating hydraulic pump of the described type, which provides the above described operational advantages achieved with the constructions disclosed in the copending applications, and which is also able to provide adequate lubrication during the initial cold operation of the engine. To achieve this objective, the present invention provides for a rapid heating of the lubricating oil and the engine to their operating temperature.